I should have made it clear that my point was in reference to using Simple Schema in conjunction with Collection2. In this case, I stand by what I said: it is an antipattern to make async calls while schema checking a document about to be inserted or modified in said MongoDB. If you can point me to a database system allowing this pattern as standard, I will stand corrected.
The rest of use cases, where Simple Schema is used for validating method arguments and other such use cases, yes, I have no comment there, though personally I avoid that too.
Nothing changes the fact that Collection2 is now being held back unnecessarily.